Conventional knitting machine cylinders generally include four main parts: a cylinder body, a sinker ring or dial, a top ring, and a plurality of metal inserts. The outer cylindrical face of the cylinder body is typically machined to form spaced-apart, radial slots in which metal inserts are individually positioned. The metal inserts extend outwardly beyond the slots to define tricks between adjacent inserts. These tricks receive the needles of the knitting machine, and act as guides for the vertical reciprocating needle motion.
The top ring is conventionally formed as a separate element which is secured to the top of the cylinder. Prior to securement to the cylinder, the top ring is typically machined to define a plurality of radial slots for receiving the sinkers. This machining process must be very precise, in order that the slots in the top ring will line up correctly with the slots in the cylinder. Thus, machining of the top ring can be time consuming and expensive.
When the top ring is secured to the top of the knitting machine cylinder, it provides support for lower surfaces of the sinkers, i.e. the bottoms of the sinker pawl, and for the backs of the needles. Because the reciprocating motions of the sinkers and needles generate large amounts of frictional forces along the wear surfaces of the top ring, it can become worn after only a minimal amount of use. Further, the tensional forces exerted by the knitted fabric being drawn down from the machine tend to localize the forces along the top ring, thereby exacerbating the problem of top ring wear.
To counter the effects of these frictional forces and minimize the resultant wear of the top ring, top rings have historically been heat treated in order to harden them so that they will be more resistant to wear. Heat treatment, however, often results in deformation of the top ring due to expansion, contraction and/or warping. As discussed above, the top ring must be precisely shaped in order that it cooperates properly with the cylinder body; thus, deformations resulting from the heat treatment of the top ring must be corrected prior to its use. Correction of such top ring defects is typically expensive and time consuming, and thus can represent a significant cost of knitting machine production and operation. Further, because these prior arrangements require machining and slotting of two individual parts, i.e. the cylinder body and top ring, manufacture of the machines tends to be relatively slow and expensive. FIGS. 1-3 depict such a typical prior art cylinder assembly for a circular knitting machine, shown generally at 10. The cylinder includes a cylinder body 12, which has a plurality of spaced-apart radially extending walls 14, between which are defined a plurality of slots 16. An insert 18 is positioned within each of the slots 16, with each of the inserts extending outwardly beyond the walls 14 to define needle-receiving channels (commonly referred to as tricks) 20 between adjacent inserts.
A top ring 22 is secured to an upper face of the cylinder body 12 such as by a screw 28 which extends through an opening 30 in the top ring and a threaded opening 32 in the cylinder body. The top ring 22 includes a plurality of upwardly extending walls 24 along its upper surface, with the walls being spaced apart to define sinker receiving channels 26. As discussed above, the top ring 22 typically provides bearing surfaces for reciprocating needles (not shown) positioned within the tricks 20 and for sinkers (not shown) which extend through the channels 26 on the top ring. Because large amounts of frictional forces tend to be produced by the reciprocating motions of the needles and sinkers, the bearing surfaces tend to wear adversely. Thus the top ring 22 is typically heat treated to harden it so that the ring is better able to withstand such frictional forces. As illustrated in FIGS. 1-3, however, the mating engagement of the top ring 22 to the cylinder body 12 must be tight and accurate in order that the moving elements of the knitting machine are properly aligned with the channels in which they reciprocate. Thus, any warping or other deformation which results from the heat treatment must be corrected before the cylinder can be effectively utilized. Also, the machined, heat treated top ring tends to be expensive to make and expensive to replace.
Other attempts have been made to overcome the deleterious effects of the frictional forces on the knitting machine cylinder. For example, U.S. Pat. No. 3,230,742 to Roedel describes a replaceable synthetic insert for increasing resistance of the inner sinker ring to frictional wear. A replaceable insert in the form of a ring is bonded by a layer of adhesive to the top of the inner sinker ring. The insert is then machined to provide guides for the sinkers and needles. Because the insert must be machined to define slots for the sinkers, the manufacturer must be particularly exact in slotting the insert in order that it will correspond appropriately to the slots containing the inserts in the outer cylindrical face of the cylinder body. Additionally, because the insert is a continuous circular band, there is no provision for any adjustment in its circumference.
U.S. Pat. No. 1,952,928 to Lawson describes a needle cylinder having a plurality of removable inserts rather than a continuous top ring. The upper edge of the needle cylinder contains grooves for frictional engagement with the inserts. The inserts are described as providing guidance for the horizontal motion of the sinkers and they may be connected by extensions to form sections of a sectional top ring. There is no provision, however, for making the individual inserts resistant to the frictional forces provided by the movement of the sinkers and needles.
U.S. Pat. No. 5,077,990 to Plath describes a friction reducing surface applied to a conventional slotted top ring of a circular knitting machine. Though this top ring is treated to reduce the amount of wear it receives, it requires the formation of slots therein. Thus, when the top ring is replaced, a new top ring must be accurately slotted to match the slots in the outer cylinder body face.
Thus, a need exists for a cylinder structure for a knitting machine which can withstand the deleterious effects of the frictional forces produced by the sinker and/or needle movements, and which can be readily and easily replaced, and which can be inexpensively fabricated.
Further, a need exists for a cylinder assembly for a circular knitting machine which can be hardened by conventional heat treatment processes and which can accommodate for slight deformations resulting from the hardening process, without requiring re-machining.